In the use of swivel units, the tendency has been to increase the mechanical load thereon because of the larger size lamps and the larger size shades required for these lamps. However, it has been found that larger loads exert large mechanical forces which act to displace the swivel unit from the position to which it was adjusted.
In order to keep the lighting fixture in its selected position, typical devices such as thumb screws, special clamps and normal screws have been used. Alternatively, springs under compression have also been used. However, in order to retain the lighting fixture in its selected position, devices using compressed springs must place these springs under a great deal of force. Devices utilizing a compressed spring are difficult to assemble and have a large number of parts. U.S. Pat. No. 3,072,426 issued to Gilbert and U.S. Pat. No. 3,409,315 issued to Wichers et al. illustrate this type of device. Another patent illustrating this type of device in U.S. Pat. No. 3,341,230 issued to Wichers.
Another type of adjustable lighting fixture known utilizes a sphere clamped between two plates, thereby causing the sphere to be under tension and allowing the sphere to rotate between the plates. A drawback with this device and many others of similar construction is that the wiring in the device is not sealed to the outside atmosphere, and therefore, if this device is used outside, moisture or rain may contact the wiring and cause a short. The swivel unit disclosed in U.S. Pat. No. 3,072,426 appears to have no exposed wires; however, to achieve this it incorporates a large number of parts thereby having the drawback of expensive assembly.
The present invention has general applicability but is most advantageously applied to a swivel unit for a lighting fixture.
The relevance of the prior art indicated in the present specification should not be given a limited interpretation. A cited prior art item may be found to have relevance in a passage other than the one referred to, or to have relevance in a sense different than as stated.